Active ray curable ink composition, active ray curable inkjet ink composition and printing method using the same   

Abstract: An active ray curable ink composition including a photoreaction initiator generating both a base and a radical through irradiation of active rays and a compound having both a functional group reactive with the base and a functional group reactive with the radical.

TECHNICAL FIELD

The present invention relates to an active ray curable ink composition, an active ray curable inkjet ink composition, and a printing method using any of the ink compositions.

BACKGROUND ART

Various printing methods are used currently. Among others, inkjet recording methods are applied to various printing fields since they can form images in a simple manner and at low cost. In general, inkjet inks used contain water as a solvent, and require exclusive paper for improving image quality. Thus, limitation is imposed on recording media employable, and also, problems such as cost elevation arise. Then, attempts have been made to develop inkjet methods applicable to recording on any recording media. Such inkjet methods include a phase transition inkjet method utilizing wax ink which is solid at room temperature, a solvent type inkjet method utilizing rapid-drying ink composed mainly of an organic solvent, and an ultraviolet (UV) inkjet method in which the ink is cured by UV light after recording.

However, printing speed has recently become higher and higher in the printing industry and, as a result, when the conventional aqueous or oily inks are employed, they may not be dried sufficiently.

To solve such a problem, active ray curable inks have been used which can be applied to any recording media and dried (cured) immediately through light irradiation.

For example, PTL 1 discloses an ink containing an alicyclic epoxy compound and at least one developing curing agent selected from an amine curing agent, an acid anhydride curing agent and an anion polymerization-type catalytic curing agent.

Also, NPL 1 discloses an ink containing a photoreaction initiator generating a base and a radical.

PTL 2 discloses an active ray curable inkjet ink employing cation polymerization and radical polymerization in combination, which contains an oxetane compound or an alicyclic epoxy compound, serving as a photopolymerizable compound, a (meth)acrylate compound, and a photoacid generator and a photoradical generator, serving as a photopolymerization initiator.

PTL 3 discloses an active ray curable inkjet ink employing cation polymerization and radical polymerization in combination, which contains a vinyl ether group-containing (meth)acrylic acid ester having in one molecule a cation-curable vinyl ether group and a radical-curable (meth)acryloyl group, and a hydroxyl group-containing polymerizable compound and/or a divinyl ether.

PTL 4 discloses an active energy ray curable resin composition containing a vinyl ether group-containing (meth)acrylic acid ester and a curable resin having at least one radical polymerizable group and/or ion polymerizable group.

PTL 5 discloses a method of curing an ink by performing radical, cation or anion polymerization reaction through plasma discharge.

Typical one of the above reaction systems is a reaction system employing a radical reactive compound and a photoradical initiator in combination. In this reaction system, although the reaction speed is high, the radials are deactivated by oxygen, so that the reaction is terminated before completion, potentially making it difficult to eliminate the residual monomer completely. Also, a reaction system employing a cation reactive compound and a photoacid generator in combination is known as one of the reaction systems that are not inhibited by oxygen. In this reaction system, the acid serving as a reactive species is not deactivated immediately, and thus, the reaction continues to proceed even after termination of light irradiation, resulting in that the residual monomer can be reduced. However, in general, the acid serving as a reactive species is a strong acid, which may disadvantageously corrode or modify a substrate. In addition, there are a few reaction systems employing an anion reactive compound and a photobase generator in combination. In these reaction systems, the reaction proceeds even by a weak base and thus, unlike the case of the cation reactive compound, corrosion does not arise. However, the reaction speed is very low, which is problematic.

PTL 1: Japanese Patent Application Laid-Open (JP-A) No. 2005-60520 PTL 2: JP-A No. 2006-213883 PTL 3: Japanese Patent (JP-B) No. 3544658 PTL 4: JP-A No. 2003-48928 PTL 5: JP-A No. 2005-523803

NPL 1: Polymer Preprints, Japan Vol. 58, No. 1 (2009), 1350

SUMMARY

The present invention solves the above existing problems and aims to achieve the following objects. Specifically, an object of the present invention is to provide an active ray curable ink composition, an active ray curable inkjet ink composition and a printing method using the same, in which the ink composition can be rapidly cured, high-quality images can be rapidly printed on various recording media, and the residual monomer can be reduced.

The present inventors conducted extensive studies and have found that the above object can be achieved by using an active ray curable ink composition containing a photoreaction initiator that generates both a base and a radical through irradiation of active rays and a compound that has both a functional group reactive with the base and a functional group reactive with the radical. The present invention can be accomplished on the basis of this finding.

The present invention is based on the finding obtained by the present inventors, and means for solving the existing problems are as follows.

<1> An active ray curable ink composition including:

a photoreaction initiator generating both a base and a radical through irradiation of active rays, and

a compound having both a functional group reactive with the base and a functional group reactive with the radical.

<2> The active ray curable ink composition according to <1>, wherein at least one of the functional group reactive with the base and the functional group reactive with the radical is a functional group reactive with both the base and the radical.

<3> The active ray curable ink composition according to <2>, wherein the compound has two or more of the functional group reactive with both the base and the radical, and at least one of the two or more of the functional groups reactive with both the base and the radical has a different molecular structure from the other functional group or the other functional groups.

<4> The active ray curable ink composition according to <1> or <2>, wherein the functional group reactive with the base is a functional group that is reactive with the base but is not reactive with the radical.

<5> The active ray curable ink composition according to <1>, wherein the compound having both the functional group reactive with the base and the functional group reactive with the radical is a compound having both a functional group that is reactive with the base but is not reactive with the radical and a functional group reactive with both the base and the radical.

<6> The active ray curable ink composition according to <4> or <5>, wherein the functional group that is reactive with the base but is not reactive with the radical is an epoxy group or a lactone group.

<7> The active ray curable ink composition according to any one of <2>, <3>, <5> and <6>, wherein the functional group reactive with both the base and the radical is a (meth)acryl group, a vinyl group, a mercapto group, a silyl group or a meleimide group.

<8> The active ray curable ink composition according to any one of <1> to <7>, wherein the photoreaction initiator is a compound represented by General Formula (I):

where B1 denotes a base, and R1 to R10 each independently represent a hydrogen atom, an alkyl group which may have a substituent, an alkoxy group which may have a substituent, an aryl group which may have a substituent, a hydroxy group, a halogen atom or a cyano group.

<9> The active ray curable ink composition according to any one of <1> to <8>, wherein the photoreaction initiator is a compound represented by General Formula (II):

where B2 denotes a base, and R11 to R18 each independently represent a hydrogen atom, an alkyl group which may have a substituent, an alkoxy group which may have a substituent, an aryl group which may have a substituent, a hydroxy group, a halogen atom or a cyano group.

<10> The active ray curable ink composition according to <8> or <9>, wherein H-B1 or H-B2 in General Formula (I) or (II) is an amidine derivative, a guanidine derivative, a phosphazene derivative or a group represented by General Formula (III) below:

where R19 to R21 each independently represent a hydrogen atom, an alkyl group which may have a substituent, a cycloalkyl group, an aryl group or an arylalkyl group, and R19 to R21 may be linked together to form a ring which may have a substituent.

<11> An active ray curable inkjet ink composition for use in inkjet printing, including:

the active ray curable ink composition according to any one of <1> to <10>.

<12> A printing method including:

coating an ink receiving material with the active ray curable ink composition according to any one of <1> to <10> or with the active ray curable inkjet ink composition according to <11>, and

irradiating the coated active ray curable ink composition or the coated active ray curable inkjet ink composition with active rays for curing.

The present invention can provide an ink composition, an inkjet ink composition and a printing method using any of these, in which the ink composition can be rapidly cured, high-quality images can be rapidly printed on various recording media, and the residual monomer can be reduced, by allowing an active ray curable ink composition and an active ray curable inkjet ink composition to incorporate a photoreaction initiator generating both a base and a radical and a compound that has both a functional group reactive with the base and a functional group reactive with the radical. These can solve the above existing problems and can achieve the above object.

An active ray curable ink composition (hereinafter may be referred to as an “ink”) of the present invention includes at least a photoreaction initiator generating both a base and a radical through irradiation of active rays, and a compound that has both a functional group reactive with the base and a functional group reactive with the radical.

One typical known active ray curable ink composition is a system containing a radical-reactive compound (radical monomer) and a photoradical initiator. The general feature of this system is, for example, that the reaction is allowed to proceed very rapidly. In the conventional cases, however, the radicals generated through light irradiation are immediately deactivated by oxygen in the air, resulting in that the reaction is terminated before completion in some cases. As a result, low-molecular-weight radical monomers remain in the ink, and problems may arise in terms of, for example, safety.

Another known system is a system containing a cation-reactive compound (cation monomer) and a photoacid generator. The feature of this system is reducing the residual monomer. This is because a strong acid (reactive species) is not degraded by oxygen (but degraded by water or a base) and the reaction proceeds even after termination of light irradiation (post-curing). However, the strong acid may problematically corrode or modify printing media.

Still another known system is a system containing anion-reactive compound (anion monomer) and a photobase generator. Similar to the case of the cation monomer, the reaction in this system proceeds even after termination of light irradiation. In addition, since a weak base can be used, corrosion or modification of printing media is difficult to occur. However, the reaction speed of this system is low and thus, for example, the printing speed cannot be set high in some cases.

In view of this, the present invention combines a radical reaction, which attains very rapid curing speed, with an anion reaction, in which the reaction speed is low but post-curing can be performed and there is no adverse effect on media. Also, the amount of the residual monomer can be reduced by using a monomer having both a radical reactive site and an anion reactive site in one molecule thereof. When the radical reaction and the anion reaction are used in combination, it is possible to attain both high-speed curing due to the radical reaction and residual monomer reduction due to post-curing in the anion reaction.

Further, use of a photoreaction initiator generating both a base and a radical tends to prevent localization of the base and radical generated. Notably, when a photobase generator and a photoradical initiator are added separately, the amount of the additives (initiators) used may be disadvantageously increased as compared with when using the photoreaction initiator generating both a base and a radical. Also, in order to increase the reaction speed, a photoradical initiator may further be added.

In order to improve jetting stability, storage stability and other properties, various additives such as a colorant may be added to the ink, if necessary. In addition, various solvents may be incorporated into the ink for the purpose of, for example, adjusting the viscosity of the ink. When the colorant is added to the ink, active rays may be difficult to reach the inside of the ink. In the conventional radical reaction systems, curing may not be completed in some cases. Meanwhile, the present invention combines the radical reaction system with the anion reaction system in which post-curing is performed. Thus, there is a possibility that even portions which active rays are difficult to reach can be satisfactorily cured.

In recent years, there has been increased desire to an on-demand system, and a high-speed, high-reliable head has been used. Then, in the printing industry, commercial printing employing the inkjet method has been increasingly performed. The ink of the present invention may be used for inkjet application.

The compound is not particularly limited, so long as it has both a functional group reactive with the base and a functional group reactive with the radical, and may be appropriately selected depending on the intended purpose. In the compound, at least one of the functional group reactive with the base and the functional group reactive with the radical is preferably a functional group reactive with both the base and the radical.

Also, the compound preferably has two or more of the functional group reactive with both the base and the radical. In the compound having two or more of the functional group reactive with both the base and the radical, the two or more of the functional group reactive with both the base and the radical may be all the same or at least one of the two or more of the functional group reactive with both the base and the radical may have a different molecular structure from the other functional group or the other functional groups. Preferably, at least one of the two or more of the functional group reactive with both the base and the radical has a different molecular structure from the other functional group or the other functional groups.

Notably, the “two or more” is not particularly limited and may be appropriately selected depending on the intended purpose. The number of the functional groups reactive with both the base and the radical is preferably 2 to 6 per compound.

Also, the functional group reactive with the base is preferably a functional group that is reactive with the base but is not reactive with the radical. The above compound is preferably a compound having both the functional group that is reactive with the base but is not reactive with the radical and the functional group reactive with both the base and the radical

Notably, per the above compound, the number of at least one selected from the functional group reactive with the base, the functional group reactive with the radical, the functional group reactive with both the base and the radical, and the functional group that is reactive with the base but is not reactive with the radical is not particularly limited and may be appropriately selected depending on the intended purpose. Thu number thereof is preferably 2 to 6.

—Functional Group Reactive with the Base—

Examples of the functional group reactive with the base include various known anion-reactive functional groups.

—Functional Group Reactive with the Radical—

Examples of the functional group reactive with the radical include various known radical-reactive functional groups.

—Functional Group Reactive with Both the Base and the Radical—

Examples of the functional group reactive with both the base and the radical include various known radical-reactive and anion-reactive functional groups. In particular, a (meth)acryl group, a vinyl group, a mercapto group, a silyl group and a maleimide group are preferred in view that the curing reaction speed becomes easily high. Specific compounds having such a functional group are those given below, but employable compounds should not be construed as being limited thereto.

Notably, examples of the compound having two or more of the functional group reactive with both the base and the radical include the following compounds (A-1) to (A-12).

Also, examples of the compound having two or more of the functional group reactive with both the base and the radical where at least one of the two or more of the functional group reactive with both the base and the radical has a different molecular structure from the other functional group or the other functional groups, include the following compounds (A-5), (A-6), (A-9) and (A-12).

—Functional Group that is Reactive with the Base but is not Reactive with the Radical—

Examples of the functional group that is reactive with the base but is not reactive with the radical include various known anion-reactive functional groups. In particular, an epoxy group and a lactone group are preferred in view that the curing reaction speed becomes easily high.

The below-exemplified compounds are compounds having the functional group that is reactive with the base but is not reactive with the radical (epoxy group and lactone group) in addition to the functional group reactive with both the base and the radical. However, employable compounds should not be construed as being limited thereto.

When the above compound has the functional group that is reactive with the base but is not reactive with the radical as described above, the unreacted portions after radical reaction are easily post-cured, which is preferred.

The photoreaction initiator is not particularly limited, so long as it generates both a base and a radial through irradiation of active rays, and may be appropriately selected from various known compounds. Examples thereof include compounds represented by General Formula (I) or (II) and photoreaction initiators described in, for example, JP-B No. 3250072 and JP-A Nos. 10-251615, 2006-282880 and 2009-244745. Among them, particularly preferred are compounds represented by General Formula (I) or (II).

where B1 denotes a base, and R1 to R10 each independently represent a hydrogen atom, an alkyl group which may have a substituent, an alkoxy group which may have a substituent, an aryl group which may have a substituent, a hydroxy group, a halogen atom or a cyano group.

Here, the alkyl group is preferably a C1-C7 alkyl group, the alkoxy group is preferably C1-C2 alkoxy group, and the aryl group is preferably C6-C10 aryl group.

where B2 denotes a base, and R11 to R18 each independently represent a hydrogen atom, an alkyl group which may have a substituent, an alkoxy group which may have a substituent, an aryl group which may have a substituent, a hydroxy group, a halogen atom or a cyano group.

Here, the alkyl group is preferably a C1-C7 alkyl group, the alkoxy group is preferably C1-C2 alkoxy group, and the aryl group is preferably C6-C10 aryl group.

H-B1 and H-B2 in General Formulas (I) and (II) are each preferably an amidine derivative, a guanidine derivative, a phosphazene derivative or a group represented by General Formula (III) below.

where R19 to R21 each independently represent a hydrogen atom, an alkyl group which may have a substituent, a cycloalkyl group, an aryl group or an arylalkyl group, and R19 to R21 may be linked together to form a ring which may have a substituent.

Here, the alkyl group is preferably a C1-C7 alkyl group, the cycloalkyl group is preferably C5-C6 cycloalkyl group, the aryl group is preferably C6-C10 aryl group, and the arylalkyl group is preferably C7-C12 arylalkyl group.

Compound H-B1 or H-B2 containing base B1 or B2 is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include primary amines such as n-butylamine, amylamine, hexylamine, octylamine, cyclohexylamine, ethylenediamine, propylenediamine, trimethylenediamine, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, diethylenetriamine, tris(2-aminoethyl)amine and pyridine; secondary amines such as diethylamine, dipropylamine, diisopropylamine, diisobutylamine, pyrrolidine and piperidine; tertially amines such as trimethylamine, triethylamine, tripropylamine, tributylamine, 1,4-diazabicyclo[2.2.2]octane and tetramethylenediamine; imidazoles such as imidazole, 1-methylimidazole, 2-methylimidazole, 2-phenylimidazole, 3-(4,5-dihydro-2-imidazolyl)pyridine, 2-benzylimidazole, 4-(4,5-dihydro-1H-imidazol-2-yl)phenylamine, 3A,4,5,6,7,7A-hexahydro-1H-benzimidazol-2-yl methyl sulfide, 2-(4-bromophenyl)-4,5-dihydro-1H-imidazole, 1-[3-(triethoxysilyl)propyl]-4,5-dihydro-1H-imidazole and DL-isoamarine; amidines such as diazabicyclononene (DBN) and diazabicycloundecene (DBU); guanidines such as guanidine, 1,1,3,3-tetramethylguanidine and 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD); a methyl-substituted product of TBD, an ethyl-substituted product of TBD, and an isopropyl-substituted product of TBD; and phosphazenes such as methylimino-tris(dimethylamino)phosphorane, t-butylimino-tris(dimethylamino)phosphorane, t-butylimino-2-diethylamino-1,3-dimethylperhydro-1,3,2-diazaphosphorine and 1-t-butylimino-hepta(dimethylamino)triphosphorane.

Specific examples of the compounds represented by General Formulas (I) to (II) include the following compounds, but employable compounds should not be construed as being limited thereto.

The amount of the photoreaction initiator added is generally about 3 parts by mass to about 15 parts by mass relative to 100 parts by mass of the polymerizable compound.

The colorant may be various known dyes and pigments. When a pigment is used, a dispersing agent may optionally be used together. Colorants excellent in light stability and color reproducibility are particularly preferred. Also, preferred are colorants which give no adverse effects on the curing reaction and which do not function as a polymerization inhibitor.

The ink receiving material usable for the present invention may be various known materials. Examples thereof include papers such as plain paper and coat paper; and non-permeable materials such as plastic films, metal and glass.

An active ray curable inkjet ink composition (hereinafter referred to as an “inkjet ink”) of the present invention contains the above-described ink.

Next, description will be given to the ink and inkjet printing method (hereinafter referred to as a “printing method”) of the present invention. The printing method of the present invention includes coating an ink receiving material with the ink and inkjet ink of the present invention and applying active rays to the ink and inkjet ink for photocuring, and can increase durability and hardness of the printed product. The active rays are appropriately selected depending on the sensitive wavelength of the photoinitiator and sensitizer, but UV rays are preferably used. The light source thereof may be various known light sources such as mercury lamps, metal halide lamps, xenon lamps and LEDs.

The present invention will next be described by way of Examples, which should not be construed as limiting the present invention thereto.

Note that the unit “part(s)” described below means “part(s) by mass.”

The materials shown in Table 1 were used to prepare ink compositions of Examples and Comparative Examples so as to have proportions shown in Table 1. The pigments used are as follows.

CB: Carbon Black pigment (product of Ciba Japan, MICROLITH Black C-K), Blue: product of Ciba Japan, MICROLITH Blue 4G-K

In Comparative Examples, the following compounds were used as the photoreaction initiator and the reactive compound.

Each of the inks of Examples and Comparative Examples was exposed to light using a high-pressure mercury lamp. The cured resin was immersed in methanol and then the dissolved matter was extracted and measured through IR for the amount of the residual monomer of the ink.

Evaluation results are shown in Table 1.

From Examples 1 to 11, the ink compositions of the present invention could be cured by a small amount of curing energy, and also, involved no residual monomer.

From Comparative Example 1, the compound having no functional group reactive with the radical needs a large amount of curing energy; i.e., rapid curing cannot be performed.

From Comparative Example 2, the ink composition containing the initiator generating no radicals needs a large amount of curing energy; i.e., rapid curing cannot be performed.

From Comparative Example 3, the ink composition containing the initiator generating no base involves the residual monomer.

TABLE 1 Residual Ink Monomer Initiator Pigment Dose monomer Ex. 1 B-1 (100) C-1 (10) — 100 Absence Ex. 2 B-2 (100) C-18 (5) — 7.2 Absence Ex. 3 B-2 (100) C-18 (5) CB (3) 20 Absence

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